Oxygenated solutions are used in a variety of applications where elevated dissolved oxygen content is desired. In the medical community, it is generally known that the effect of oxygen on living tissue can be characterized by three regimes, namely, metabolic enhancement (growth accelerator), metabolic inhibition (growth arrest), and toxicity. In the former regime, oxygenated solutions can be used to accelerate the healing and regeneration rate of damaged tissue. Such wounds include cuts, lacerations, sores and burns on the face, arms, legs, torso and roof of the mouth. When wounds begin to heal, fibroblastic cells divide and spread throughout the wound area. The fibroblastic cells produce collagen, an important protein that facilitates healing. Supplying sufficient quantities of oxygen to the wound area significantly enhances fibroblast proliferation. In particular, the fibroblastic cells use amino acids hydroxylated with oxygen to synthesize collagen chains. In addition to treating wounds, oxygen is frequently used in topical applications for cleaning and revitalizing skin. In facial cleansing, dissolved oxygen assists in exfoliating dead skin particles from the skin surface. Dissolved oxygen has also been used to remove toxins, particulates and other occlusions in skin pores. In addition, oxygen has been used to revitalize skin cells by joining with protein molecules to nourish the cells and produce collagen.
The amount of oxygen initially dissolved into solution is largely dependent on the method used to dissolve the oxygen gas into solution. One common method for oxygenating water is the coarse bubble aeration process, which is a subset of aeration methods known categorically as air diffusion. Pressurized air or oxygen gas is introduced through a submerged pipe having small holes or orifices into a container of water. Gas pressure is sufficient to overcome the hydrostatic head pressure, and also sustains pressure losses during passage through the small gas orifices. As a result, bubble aeration occurs at relatively low pressures; this pressure being predominantly a function of tube immersion depth.
Since all interphase interfaces have a characteristic surface energy, the creation of interfacial (surface) area is an energetic process. As a gas passes through an orifice, for example, pressure energy is converted to kinetic energy, which consequently satisfies the energetic requirements of the system for the production of surface area. Area and velocity are inversely proportional; hence, as the orifice diameter decreases, the corresponding pressure drop and gas velocity increase, and more surface area is generated. Smaller bubbles result. This process has a limiting condition, however, in that the amount of heat (as irreversible work) that is produced is inversely proportional to the square of orifice diameter. It therefore becomes impractical and energetically inefficient to operate at exceptionally small orifice diameters. This process also has an absolute limit as a gas velocity of Mach one is approached within the pore. Because a pore lacks the convergent/divergent geometry required to achieve supersonic flow, increasing pressure beyond the critical pressure will not result in a further reduction of bubble size.
Since oxygen therefore is introduced into solution at relatively low pressures in the bubble aeration process, the oxygen bubbles are relatively large. As a result, the aggregate bubble surface area for a dispersion of bubbles produced by bubble aeration is relatively small. The limited surface area produced by bubble aeration limits the concentration of gas that can be dissolved into solution. Oxygen dissolution is a function of the interfacial contact area between gas bubbles and the surrounding medium, and bulk fluid transport (mixing) in the liquid phase. In particular, the rate of oxygen dissolution is directly proportional to the surface area of the bubbles. A dispersion of very small bubbles, e.g. bubbles having diameters in the order of 50 microns, will have a much larger total surface area than a dispersion of large bubbles occupying the same volume. Consequently, the rate of oxygen dissolution in bubbling aeration is limited by the size of the bubbles introduced into the solvent. Fluid mixing is also very limited in bubbling aeration because the only energy source available for agitation is the isothermal expansion energy of oxygen as it rises in the solution.
Oxygen dissolution in bubbling aeration is also limited by ambient pressure conditions above the solution. If the solution being aerated is exposed to atmospheric conditions, the dissolved oxygen concentration will be limited to the solubility limit of oxygen (at its partial pressure in air of 0.21 atm) under such conditions. The desirability of bubbling aeration is further hampered by equipment and energy requirements. Large blower units are used to force the gas bubbles into the carrying liquid. These blowers generate high-energy costs and often require special soundproof installations or other engineering costs.
Hydrogen peroxide is another popular source of oxygen used in topical applications and baths. Oxygen is easily derived from hydrogen peroxide, or H2O2, because an H2O2 molecule readily dissociates into water (H2O) and an oxygen free-radical. The decomposition of H2O2 into water and oxygen free-radicals creates an enriched solution that facilitates dermal contact with oxygen. Hydrogen peroxide is distributed in various grades and concentrations that are specific to certain applications. Solutions of 3% and 6% hydrogen peroxide are commonly sold to consumers who use the solutions to disinfect cuts and clean skin areas. Solutions of 35% hydrogen peroxide are frequently added to spas and hot tubs to disinfect the water. Skin therapists use solutions of 35% hydrogen peroxide in oxygen baths to improve tissue regeneration and remove toxins from the dermis. Some topical creams contain stabilized forms of hydrogen peroxide intended to prevent free-radical formation and infections in skin.
Despite being a significant source of oxygen, hydrogen peroxide has been the subject of significant controversy when used in skin treatment applications. Some authorities claim that hydrogen peroxide is cytotoxic to human fibroblasts, due to the presence of free-radical oxygen. As a result, some medical professionals recommend additional dilution of hydrogen peroxide solutions to avoid their toxic effects on skin. Authorities also state that hydrogen peroxide reduces white blood cell activity. Still others have found that hydrogen peroxide slows wound healing by drying the wound, which destroys the exudate and leads to necrosis of skin tissue. Dry tissue also makes the wound area prone to bacterial growth and infection. As a result, hydrogen peroxide has drawn some questions as to its suitability for treating skin wounds and burns.